Method for manufacturing a panel including a reinforcement sheet

ABSTRACT

A method for manufacturing a panel, the panel having a thickness in a range of 1.5 to 6.5 mm and including at least one substrate layer and a printed decoration layer covered by a protection layer. The method includes the steps of providing a granulate containing PVC and fillers, and having a cylindrical shape with a cylinder diameter in the range of 2.5 to 3.5 mm and a cylinder height in the range of 0.2-2.0 mm, melting the granulates and forming the substrate layer by means of molten granulates. The layer have a thickness of 1 to 3.5 mm. The method also includes forming a laminated complex by applying the printed decoration layer and the protection layer to at least the substrate layer by laminating or coating.

The present invention relates to a method for manufacturing a panel,such as a floor panel, including a reinforcement sheet, comprising thesteps of providing a first layer of thermoplastic material, providing areinforcement sheet, laying the reinforcement sheet and the first layeronto each other, applying a second layer of thermoplastic material ontothe reinforcement sheet at a side facing away from the first layer, atleast partially melting the thermoplastic materials of the first layerand the second layer, and adhering the at least partially melted firstlayer, the at least partially melted second layer and the reinforcementsheet to each other so as to form the panel.

Such a method is known in the field of plastic floor products includinga reinforcement sheet.

Patent application US-A-2007/0166516 describes a typical method forproducing (mainly plastic) modular floor products by calandering andlaminating techniques. According to this method several continuous sheetor foil shaped layers are produced by calandering, after which theselayers are laminated together using a continuous laminating process. Inthis laminating process several layers are consecutively added, startingwith one or more substrate layers, including a balance sheet, and onwhich a printed layer is added, followed by a transparent layer. This isdone in one single production process with a series of laminating niprolls, where upfront each laminating roll a new layer is unwound from aroll, preheated and pressed on the previously laminated layers.

-   -   It is also described to add a glass fiber based web in the        product. This glass fiber web can be a non woven, a grid, or a        scrim (combination of non woven and grid) and gives an excellent        dimensional stability to the product.

The glass fiber can be added in the laminating line, where it is adheredto a previous calandered layer, after which another calandered layer isadded on top of this complex, after which further layers can be added.The glass fiber web can be added in an untreated form, but can also bepretreated in an offline step with a coating, in order to assure abetter connection. In an alternative offline step the glass fiber webcan be impregnated on a calandering line, where in one step a calanderedlayer is produced from a molten thermoplastic material, on which theglass fiber web is immediately added, in a laminating nip roll. Thisintermediate complex can then be combined with the other necessarylayers on a laminating line.

A critical process step in the known production steps is sufficientimpregnation of the glass fiber web at high line speeds. In thesecontinuous processes contact time at the nip roll, in which the glassfiber web and plastic layer are laminated and/or impregnated, is soshort that there is a risk the impregnation is not done properly,leading to delamination of the layers from the glass fiber web in thefinished product during further converting steps or during use of theproduct. One way to overcome this is to pre-impregnate the fiber with acoating. This however increases the cost of the final product, requiresan extra offline operation, and can also change the final properties ofthe product like bending stiffness.

Another method for producing modular floor products is described inpatent application WO 2013/179261 A1. According to this method agranulate of a thermoplastic material is spread on an endless belt,which makes part of a double belt press, a glass fiber layer is appliedon this spread layer, and another granulate layer thermoplastic materialis spread on top of the glass fiber layer, wherein in a subsequent stepboth layers, including the glass fiber layer are compressed in thedouble belt press. The belts also assure melting of the thermoplasticmaterial due to heating energy supplied through a lower and upper belt,and impregnating the glass fiber layer, in order to obtain a glass fiberreinforced continuous plastic slab, typically to be finished to floorpanels.

Also in this method the glass fiber gives a good dimensional stabilityto the finished product.

The problem of a critical impregnation process of the glass fiber ispartially overcome, since contact time between plastic material andglass fiber is longer, so that impregnation can be assured. A drawbackof this system however is a possible damaging of the glass fiber. Due tothe embedding of the glass fiber between two layers of granulate, andthe compression in a double belt press, individual granulates canlocally deform the fiber or even perforate it. A careful balance needsto be found between melting, and pressure in the press. Due to this thedouble belt process is not at all flexible to perform a rapid changeoverin product thickness, glass fiber type, formulations, or the like. A wayto partially overcome the problem of deformation, or perforation of theglass fiber, is to use very fine granulate (microgranulate), typicallyto be made in a pelletizing extruder. The production of thesemicropellets is also difficult, since output decreases when decreasingthe pellet diameter, leading to higher investment for the extruders.When the pressure becomes too high, there is more chance on burntmaterial.

The object of the invention is to provide a method for manufacturing apanel including a reinforcement sheet, which method eliminates theabove-identified drawbacks.

This is achieved by the method according to the invention, which ischaracterized in that the reinforcement sheet and the first layer areadhered to each other by pressing them together after at least partiallymelting the thermoplastic material of the first layer, but beforeapplying the second layer of thermoplastic material onto thereinforcement sheet.

This means that during the step of pressing the risk of deformation ofthe reinforcement sheet by for example individual granulates in thefirst layer is minimized, since the second layer is not present yet.Particularly, if the second layer was present and softened due to atleast partially melting it, the reinforcement sheet could be deformedand/or damaged during pressing due to granulates of the first layer thatare not yet softened enough. In the method according to the inventionthe reinforcement sheet and the first layer are pressed together beforeapplying the second layer, which means that the reinforcement sheet canbe supported directly by a rigid press element, such as a press plate ora press belt, which minimizes the risk of deformation and/or damage ofthe reinforcement sheet.

The resulting product may be further treated to obtain a flooringproduct having a thickness which is typically within a range of 1.5-6.5mm, and preferably between 2 mm and 5 mm.

The first layer, situated at the backing of the finished product, andwith the reinforcement sheet typically positioned in the middle of theproduct, will finally be in the range of 1-2.5 mm. For reasons ofavoiding upward curling of the resulting product, the reinforcementsheet can also be positioned in another height position than in themiddle of the final product. For example, its position may be locatedsuch that the product is naturally bent upwardly to a limited extent,but due to its own weight, it will lay flat on the ground. In this wayit is assured that there will be no upstanding edges, which is notdesired by the customer. When the reinforcement sheet is positionedhigher, the thickness of the first layer can typically be between 1.25and 3.5 mm after pressing.

It is noted that the first layer and the second layer are attached tothe reinforcement sheet through adhering properties of the respectivemelted thermoplastic materials.

In a practical embodiment the first layer of thermoplastic material isprovided in the form of granulates which are spread and subsequently atleast partially melted and/or the second layer of thermoplastic materialis provided in the form of granulates which are spread and subsequentlyat least partially melted.

In a specific embodiment the first layer of thermoplastic material isprovided in the form of granulates which are spread and subsequently atleast partially melted and the second layer of thermoplastic material isprovided in the form of a sheet or film. The sheet or film may bepressed separately, for example from granulates, and may still be atleast partially melted before applying it onto the reinforcement sheet.

The first layer and the second layer are adhered to the reinforcementsheet upon bringing them in close contact to each other. The first layerand the reinforcement layer are pressed to each other, but in a nextstep the second layer may be brought in close contact to thereinforcement layer without pressure or at a pressure which is lowerthan the pressure that is applied for pressing the first layer and thereinforcement layer to each other.

A typical thermoplastic granulate is made of flexible or semirigidpolyvinyl chloride (PVC), but can also be rigid PVC. Other possiblepolymers are polyolefines like polypropylene, polyurethane, rubber basedcompounds, elastomers, or mixtures of polymers like elastomer andpolypropylene, or wood plastic composites, being mixtures including woodflour or particles and polymer.

The first layer of thermoplastic material may be made of semi rigid PVCcontaining at least 35% of inorganic fillers.

It has been demonstrated by the inventors that for the whole thicknessrange described above, more specific also for a relatively thin layer of1 mm, it is possible to use a standard granulate size with a granulatediameter of 3.2 mm. When using this standard granulate diameter of 3.2mm, the best result of evenly pressed surface with very narrow thicknesstolerances of the pressed layer, was given by adjusting the length ofthe granules to 0.5 mm, creating a short cylindrical shape. The shortcylindrical shape is not putting constraints to the production of thegranulate. It only needs a faster cutting speed at the extruder head,where the melt is extruded through a perforated plate. The typical sizeof 3.2 mm is a standard in the thermoplastic industry, and allows to runthe extrusion process at high outputs, without creating high backpressures. High back pressures easily create burning of shear sensitivematerials like PVC, due to which output then would need to be decreased,leading to higher production or investment costs.

Preferably, the method is performed as a continuous process, resultingin a continuous sheet which can be cut into panels of any desired sizeafterwards. The panels may then be further provided with coupling meansfor coupling panels to each other so as to form a covering. For example,edges of the panels may be provided with tongues and grooves.

The reinforcement sheet and the first layer may be pressed together bymeans of a double belt press. This creates an even force distribution ofthe reinforcement sheet on the first layer.

It has in particular been found by the inventors that by applying thereinforcement sheet on top of the spread first layer, the upper beltprotects the reinforcement sheet against deformation or perforationthrough the granulate, no matter what pressure is used. Hence even athigh pressures, and even when the granulate is not reaching thetemperature at which it becomes completely thermoplastic so that it canbe shaped, the reinforcement sheet will remain intact.

It has been shown to be an advantage of this particular process ofspreading a layer and compressing this layer with the reinforcementsheet backed up by the upper belt of the double belt process, to be ableto run with the standard granulate diameter of 3.2 mm, and not needingsmaller granulate or microgranulate.

The granulates may have a cylindrical shape with a cylinder diameter inthe range of 2.5-3.5 mm and a cylinder height in the range of 0.2-2.0mm. A height of about 0.5 mm is preferred.

Additional layers may be applied on the first layer and the secondlayer, such as a backing layer on the first layer, and a printeddecoration layer on the second layer, possibly covered with a protectionlayer. This may be accomplished by a laminating or coating process.

Additional steps may be included, such as embossing of top and/or bottomside of the laminated complex, applying a UV lacquer on the top side,and cutting this material in slabs for further converting to finishedmodular floor elements.

The second layer of at least partially melted thermoplastic material onthe reinforcement sheet may be pressed onto the reinforcement sheet bymeans of calandering. This is a relatively simple process.

A particular advantage of the calandering process, is that thecalandered second layer is levelling the thickness of the obtainedproduct. A levelling is often needed because the mechanical tolerancesof the double belt press are limited to 0.1 mm. A typical prior artlevelling operation is done by sanding the pressed surface. For thissanding operation the substrate needs to be cooled. This however iscomplicated, requesting for extra space, investment, and energy cost,since the product coming out of the press needs to be cooled to atemperature at which it can be sanded. This is undesired, however, sinceit needs to be heated up again when a decorative layer and/or protectivelayer need to be applied.

The calandering process may be performed by a calandering device whichcomprises more than two calandering rolls, for example between two andfive calandering rolls.

The second thermoplastic layer, applied with a calendar on the abovedescribed complex of pressed granulates and reinforcement sheet, istypically flexible or semi-rigid polyvinyl chloride (PVC), but can alsobe rigid PVC. Other possible polymers are polyolefines likepolypropylene, polyurethane, rubber based compounds, elastomers, ormixtures of polymers like elastomer and polypropylene, or wood plasticcomposites, being mixtures including wood flour or particles andpolymer.

The thermoplastic material of the first layer and the second layer maybe the same, or can be based on the same polymer, but having a differentrecipe, or can be based on a different thermoplastic material.

The reinforcement sheet may comprise a glass fibre foil, preferablyhaving a weight of 25-70 g/m2.

The inventors have found that a variety of glass fibers can be used inthis method with good result. In general higher weight fibers lead tolower permeability, hence more difficult impregnation and processstability, but better dimensional stability. In the state of the artlaminating or pressing methods, applying a big part of this range ofglass fibers leads to bad impregnation results and/or difficult productchangeovers between thin and thick products. With the method describedherein, glass fibers could be used between 25 and 70 gram per squaremeter with very good results.

High production speeds could be obtained, with fast and drastic productchangeovers between total product thicknesses of 1.5 and 5 mm.

It is advantageous when during the step of pressing the reinforcementsheet and the first layer to each other, the reinforcement sheet isimpregnated by the thermoplastic material of the first layer over atleast 80% of its thickness. This can be controlled by selecting at leastan appropriate pressure and temperature during the pressing step.Additionally, residence time in a press may influence the rate ofimpregnation.

The invention is also related to a floor panel which is made accordingto the method as described hereinbefore. Other panels for alternativeuse are conceivable, such as panels for inside or outside use, for wallcovering, ceiling covering, or the like.

The invention will hereafter be elucidated with reference to a veryschematic drawing showing an embodiment of the invention by way ofexample.

FIG. 1 is an illustrative side view of an apparatus for performing anembodiment of the method for manufacturing a panel according to theinvention.

FIG. 1 shows a part of an apparatus 1 for continuously processing a weband illustrates some steps of an embodiment of a method formanufacturing a panel including a reinforcement sheet according to theinvention. The apparatus 1 includes a granulate supply 2 which isadapted to supply a first layer or base layer 3 of granulate on asupporting lower conveyor belt 4. The lower conveyor belt 4 is anendless belt. The granulate is spread evenly on the lower conveyor belt4. The granulate is made from a thermoplastic material, for exampleflexible PVC.

The lower conveyor belt 4 has a greater length than a second, upperendless conveyor belt 5 which is positioned at a distance downstream ofthe granulate supply 2 and runs along a part of the lower conveyor belt4. At the upper portion of the lower conveyor belt 4, both conveyorbelts 4, 5 run in the same manufacturing direction, in FIG. 1 from leftto right as indicated by an arrow at the lower conveyor belt 4.

There is supplied a reinforcement sheet 6 on top of the base layer 3 ofgranulate. The reinforcement sheet 6 may be a glass fibre foil or anyalternative foil which has reinforcement properties. The reinforcementsheet 6 is supplied by unwinding it from a supply roll 7. Subsequently,the reinforcement sheet 6 and the base layer 3 of granulate aretransported between the lower and upper conveyor belts 4, 5 along aheating device 8 in order to melt the base layer 3 of granulates, andthen pressed together by a pressing unit 9. The rate of melting may besuch that the granulates are fully converted into a pasty substance, butit is also conceivable that the granulates are partially melted. Thereinforcement sheet 6 and the base layer 3 are attached to each otherunder pressure through adhering properties of the melted thermoplasticmaterial. Subsequently, the base layer 3 including the reinforcementsheet 6 are transported along a cooling unit 10. It is advantageous thatthe reinforcement sheet 6 is directly supported by a rigid press elementof the pressing unit 9, since a soft layer between the reinforcementsheet 6 and the rigid press element would increase the risk ofdeformation or damage of the reinforcement sheet 6 by granulates of thefirst layer 3 that are not fully melted. It provides the opportunity toapply relative large granulates in the base layer 3.

In a next step a second layer or top layer 11 is provided on top of thereinforcement sheet 6. The top layer 11 is made from the samethermoplastic material as the base layer 3, but this may be different inan alternative embodiment. The thermoplastic material of the top layer11 is melted and pressed into a sheet by nip rollers, and the still atleast partially melted sheet 11 and the base layer 3 including thereinforcement sheet 6 are then pressed together by means of calanderingrolls 12, resulting in a web having a smooth upper surface.

At a position downstream of the calandering rolls 12 there may bearranged a cutting mechanism (not shown) to cut the resulting continuousweb into separate panels which are then collected for furtherprocessing.

In an alternative embodiment (not illustrated) the reinforcement sheetmay be placed on top of a lower press plate or press member in a firststep, after which thermoplastic granulates are spread over thereinforcement sheet to form the first layer. The granulates may be atleast partially melted before or after spreading. Subsequently an upperpress plate or press member is placed on top of the first layer and thelower and upper press plates or press members can press the first layerand the reinforcement sheet to each other. The resulting intermediateproduct may be turned upside down and the second layer of thermoplasticmaterial, for example an at least partially melted sheet, can be appliedon top of the reinforcement sheet at its side facing away from the firstlayer. In case of placing an at least partially melted sheet on top ofthe reinforcement sheet, this can be fixed thereto by means ofcalandering. It is also possible that the resulting intermediate productis not turned upside down and that that second layer is applied onto thereinforcement sheet when the reinforcement sheet extends below the firstlayer.

From the foregoing, it will be clear that the invention provides animproved method for manufacturing a panel including a reinforcementsheet.

The invention is not limited to the embodiment shown in the drawing anddescribed hereinbefore, which may be varied in different manners withinthe scope of the claims and their technical equivalents. For example,the first layer may be applied on the lower conveyor belt in meltedcondition instead of first spreading and then melting the granulates.Furthermore, heating of the granulates of the first layer may beperformed before laying the reinforcement sheet and the first layer ontoeach other.

1-15. (canceled)
 16. A method for manufacturing a panel, said panelhaving a thickness in a range of 1.5 to 6.5 mm and comprises at leastone substrate layer, a printed decoration layer covered by a protectionlayer, wherein said method comprises the steps of: providing a granulatecontaining PVC and fillers, and having a cylindrical shape with acylinder diameter in the range of 2.5 to 3.5 mm and a cylinder height inthe range of 0.2-2.0 mm; melting said granulates and forming saidsubstrate layer by means of molten granulates, said layer having athickness of 1 to 3.5 mm; forming a laminated complex by applying saidprinted decoration layer and said protection layer to at least saidsubstrate layer by laminating or coating.
 17. The method of claim 16,wherein said granulate comprises at least 35% of inorganic fillers. 18.The method of claim 16, wherein granulate is provided by melting amixture of PVC and fillers, extruding the mixture through a perforatedplate, and cutting the extrudate every 0.2 to 2.0 mm.
 19. The method ofclaim 16, wherein the panel further comprises a reinforcement sheetpositioned on top of said substrate layer
 20. The method of claim 16,wherein said substrate layer is provided in the form of said granulateswhich are spread and subsequently at least partially melted.
 21. Themethod of claim 16, wherein said substrate layer is provided in moltencondition on a conveyor belt.
 22. The method of claim 16, wherein saidPVC is semi-rigid PVC.
 23. The method of claim 16, wherein said methodis a continuous process in which at least said substrate layer is formedas a continuous sheet
 24. The method of claim 16, said method furthercomprising the step of embossing said laminated complex.
 25. The methodof claim 16, said method further comprising the step of applying a UVlacquer on the top side of the laminated complex.
 26. The method ofclaim 16, said method further comprising the step of cutting thelaminated complex in slabs for further converting to finished modularfloor elements.